Organic finish remover and method



2,975,140 ORGANIC FINISH REMOVER AND METHOD William L. Yaroch, deceased,late of SouthfDearborn, Mich., by Geraldine Yaroch, administratrix,Garden City, Mich., assignor to Klem Chemicals, Inc., Dearborn, Mich., acorporationof Michigan No Drawing. Original application July 27, 1954,Ser. No. 446,151. Divided and this application Nov. 29, 1957, Ser. No.712,603

14 Claims. (Cl. 252-110) This invention relates generally to an improvedprocess for removing paints and synthetic coatings and compositionstherefor, and more particularly toa composition and method for strippingpaints, enamels, synthetic resin coatings and other organic finishesfrom metals and the surfaces of other materials. This application is adivision of my co-pending application Serial'No. 446,151, filed July 27,1954, for Organic Finish'Remover and Method and a continuation-in-partof Serial No. 103,951, filed July 9, 1949, for Cleaning SolutionforRemoving Organic Finishes, both now abandoned.

t In industrial production of automobiles, refrigerators, stoves andmany similar commercialarticles, a highly resistant and durable finishis applied to beautify and pro tect the same. Over the past years, thesefinishes have been greatly improved in regard to resistivity againstattack by solvents and against other damage. At present, and in contrastto finishes in common use about years ago, these finishes are highlycomplex in chemical structure, frequently containing synthetic resinshaving widely varying chemical structures and properties.

In the-manufacture of the above articles, particularly when using massproduction techniques, it is frequently necessary to remove the finishfrom imperfect or damaged articles. In normal operation, a certainpercentage of the finished articles have flaws and require reprocessing,necwsitating removal of the highly resistant finish.

' United States Paten'tfO In addition, it is frequently desired torefinish painted articles, in which event it also is necessary or highlydesirable to remove the original finish.

Prior to this invention, a large number of cleaning solutions have beensuggested containing as a major ingredient sodium hydroxide or otheralkali metal hydroxide.

Frequently, these alkali metal solutions contain-additives, such ascresylic acid or other phenolic compounds, Other cleaning solutions havealkali metal hydroxides; modified with water softening agents,dispersing agents,

and suspending agents, such as various complex phos- 1 phates,silicates, and the like. The above discussed cleaning materials, whilesuitable for paints and other finishes in common use several years ago,are entirely unsuitable for many of the improved finishes presently ingeneral use. In particular, they require excessively high concentrationsof the alkali metal hydroxides which are hazardous, inconvenient, anddisagreeable to use. Stripping operations using the above materialsrequire long periods of contact of the finish with the cleaningsolution, resulting in low production and increased cost of operations.In general, to effect attack of the finish by such prior cleaningsolutions, high temperatures are required which increase the cost ofoperation and equipment. However, of primary importance, the above priorcleaning solutions do not remove a thin deposit of finish componentswhich adhere tenaciously to the surface of the article and which must beremoved prior to refinishe ing the article. In consequence, this depositmust be removed manually, which increases considerably thetime P 2 975Patent d and cost involved in the reclaiming of imperfect parts orarticles.

In employing prior cleaning solutions for removing many present dayfinishes, after the bulk of the finish has been removed by the solution,the article or part must be brushed or rinsed several times to obtain asuitably clean surface, such as is necessary for refinishing thearticle. However, even after such repeated mechanical operations, thesurface is not entirely free from foreign materials, which materialsadversely aflfect the adherence of any subsequent finish. It appearstherefore that the alkaline stripping compounds previously in use do notcompletely breaker otherwise sever the adherent bond between thefinished surface and the finish itself.

It is therefore a principal object of this invention to provide animproved cleaning solution and method for removing organic finishes suchas paints, enamels, synthetic coatings and similar finishes. It isanother object of the present'invention to provide a composition of theabove type and method which will leave the surface of the article orpart in suitable condition for refinishing without-the necessity ofadditional cleaning operations, such as brushing, scraping and the like.Another object of this invention is to provide a cleaning compositionand method which will completely remove a large variety of finishes in aminimum period of time, at relatively low temperatures and whileemploying a minimum concentration of alkali metal hydroxide. Anotherobject is to pro vide a continuous process adaptable to mass productiontechniques. Other objects of the invention will appear in the followingdescription and appended claims.

Before explaining the present invention in detail, it is to beunderstood that this invention is capable of other embodiments and ofbeing practiced or carried out in various ways. It is also to beunderstood that the phraseology or terminology employed herein is forthe purpose the gluconic acid or its derivative is particularlysunpris-J ing in that solutions of gluconic acid have no effect on suchfinishes, in the absence of an alkaline metal. However, when combinedwith an alkali metal, the resulting solution is considerably morereactive to organic finishes than the alkali metalv hydroxide itself.With SUChSOIU'. tions, the time of stripping is considerably reduced,lower temperatures of operation are possible, lower concentrations ofalkali metal hydroxide are permissible, but of primary importance, noresidual film or composition remains on the surface of the part whichnecessitates brushing, scraping or other operations prior to refinishingof the article or part. finished article to an alkali metal solutioncontaining a soluble gluconate, the part or article from which thefinish is removed only requires at most a simple'waten rinse or wash andthe so-treated surface is immediately ready for refinishing.

Of particular importance is position of this invention, containinggluconic acid, for many synthetic resin coatings which were entirely-re:sistant, or practically resistant to prior paint remover compositions.Included in such coatings arealkyd resins, modified alkyd resins, suchas styrenated 'alkyds;

urea formaldehyde resins, melamine resins, metallic type paints,silicone resins,v epoxy resins and the like.-;."..- -..':f*

It has'alsobeen found-that when-the abovecleaning Instead, aftersubjection of the the activity of the comsolution, i.e. containing analkali metal hydroxide or basic salt thereof containing small quantitiesof a soluble gluconate, is modified with an organic nitrogen-containingbase, e.g. an amine that the activity of the cleaning stolution isadditionally increased. Such amines, when added to the abovegluconate-containing solution attack many finishes heretofore resistantto chemical attack and, in general, decrease the time required forstripping the finish, permit lower temperature operation and lower thepermissible alkali metal hydroxide concentration.

When using the cleaning solution and process of the present invention,the finish is attacked in a manner in which the bond at the inner faceat the surface and finish is broken so as to completely free the finishfrom the surface. In consequence, after attack of the finish by thepresent cleaning solution, the finish particles can be easily andreadily washed from the surface by simply spraying or flushing withwater.

In operation, the alkali metal-gluconate solution, with or without aquantity of an amine, can be sprayed onto the finish to be removed orthe articles having the finish to be removed can be immersed directly ina bath containing the cleaning solution. After contacting the finishwith the improved cleaning solution of this invention, the part orarticle is then washed or sprayed with water to remove any traces orparticles of removed finish. The article is then in condition forrefinishing, if desired.

When using the composition and process of this invention for large scaleoperation, the parts or articles are preferably passed on a conveyorthrough a cleaning vessel having spray jets directing a stream of thecleaning solution on the surfaces to be removed. The cleaning vessel canalso be provided with Water jets to rinse the articles and also means todry the cleaned articles, if desired.

The alkali metal hydroxides and basic salts thereof suitable for thisinvention are sodium hydroxide, potassium hydroxide, lithium hydroxide,rubidium hydroxide, cesium hydroxide and basic salts thereof, such asthe carbonates, silicates, and phosphates. In addition to these, thesolution can also contain soaps, resinates, or synthetic organic surfaceactive agents and other water softening, sequestering, dispersing, orsuspending agents.

The soluble gluconate can be added to the solution in any suitable form,such as gluconic acid, glucona delta lactone, sodium gluconate,potassium gluconate, or any other soluble salt of gluconic acid, or itcan be added in a combined form with any of the organic nitrogencontaining bases discussed in detail below. For example, gluconic acidcan be first treated with aniline to produce aniline gluconate and thelatter added to the alkali metal hydroxide.

The concentration of the alkali metal hydroxides can vary depending uponthe types of finish, the quality of the paint bond, the temperature ofthe cleaning solution, and the time of contact of the finish with thecleaning solution. In general, the concentration should be between about3-50 percent, based on the total weight of the solution. A more desiredconcentration of alkali metal hydroxide is between about 8-35 percent byweight of the total solution although the preferred concentration isbetween about 15-25 percent, based on the total weight of the solution.

The concentration of the gluconic acid should be above 0.05 percent byweight of the total solution. If a derivative of gluconic acid isemployed, equal molar quantities of gluconate are employed. Relataivelyhigh concentrations can be used advantageously, although above 10percent there is generally no appreciable increase in effectiveness. Thehigher concentrations of the gluconate are usually desirable when it ispreferred to employ minimum concentrations of the alkali metalhydroxide. The preferred concentration of gluconate compound is betweenabout 0.3-3.0 percent by weight of the weight of the alkali metalhydroxide.

2, QJAO.

As noted above, amines and certain other nitrogen containing compoundsused with an alkali metal and gluconic acid or salt thereof furtherimproves the reactivity of the solution toward paints, enamels,synthetic resins and other coatings: The amine compounds suitable forthis invention are either aliphatic or aromatic, the latter beingpreferred. Of the aliphatic amines, the compound can be either primary,secondary or tertiary. Examples of such amines are ethylamine,dipropylamine, and tributylamine. In addition derivatives of ammoniumhydroxide are also suitable, for example, tetramethyl ammoniumhydroxide.

The preferred aromatic organic nitrogen-containing bases can either becyclic or heterocyclic with the latter being preferred. Of the cyclicamines, either a monoring or multi-ring compound is suitable. Typicalexamples of such cyclic amines are aniline and benzidine. The preferredheterocyclic amine compounds also can be mono-ring or multi-ring, themono-ring being preferred. Typical examples of the mono-ringheterocyclic amine compounds are furfurylamine, pyridine, andmorpholine. In regard to activity, the furfurylamine is the mostpreferred. However, morpholine is also very effective and iscommercially available in relatively large quantities at the presenttime. The multi-ring heterocyclic aromatic compounds suitable for thisinvention are acridine and other similar compounds.

The amine radical can also be substituted with an organic radical. Forexample, monoisopropanol amine, diisopropanol amine and triisopropanolamine are very effective.

Polyamines are also useful in accordance with the present invention. Asexamples, urea and dipropylene triarnine are very effective. Thio-amineand cycle amines can also be used. An example of an effective thio-amineis diethylthiourea and examples of cyclo amines are cyclohexyl amine andhexamethylene tetramine.

Nitriles such as acetone cyanohydrin are also suitable for thisinvention. Also, certain amides have also been found effective, forexample, butyramide.

The concentration of the amine can vary between 0.5 and 1.5 moles permole of gluconate compound employed. Preferably, a 1:1 mole ratio ofamine and gluconate compound is employed.

With the present invention, a finish can be removed from a surface, suchas a metal surface, not deleteriously attacked by the cleaning solutionof this invention, by immersion of the surface in a vessel containingthe alkali metal hydroxide and a soluble gluconate, with or Without anamine. The finish is maintained in contact with the cleaning solutionfor a time sufficient to break the bond between the finish and thesurface of the part or article and, if necessary, is thereafter rinsedor sprayed with Water to remove all of the finished components. Ingeneral, the time of contact required is between and 30 minutes, butnormally, does not exceed five (5) minutes. Alternatively, the finishcan be sprayed with the cleaning solution of this invention, in whichcase a water rinse is frequently unnecessary.

The temperature of the above solution can be varied between roomtemperature and the boiling temperature thereof, although, in general,it is preferred to use higher temperatures so as to decrease the time ofcontact of the finish with the cleaning solution. In any event, however,the present cleaning solution reduces the contact time when operatingeither at lower or higher temperatures.

The process of this invention has important application to a widevariety of surface coatings or finishes. As pointed out above, thepresent process is of particular importance in removing finishes formedfrom the synthetic resins, due to their resistance to strong alkaliesand paint remover compositions heretofore known. lncluded in suchsynthetic resins are phenolforrnaldehyde, urea formaldehyde, maleic,coumarone-indene, silicone,

epoxy and vinyl resins. Of peculiar importance, due to their extensivecommercial useare the alkyl resins, and so-called modified alkyd resins.As is well known, the alkyl resins are condensation products ofpolyhydric alcohols and polybasic acids, Glycerol is presently the mostwidely used polyhydric alcohol, although ethylene,

diethylene and tr-iethylene glyco'ls, sorbitol, mannitol,

and pentaerythritol can also be used. Of the polybasic acids, phthalicanhydride is the most important; Other acids are succinic, adipic andsebacic.

Urea-modified alkyds or blends of urea-formaldehyde resins withoil-modified alkyds are frequently used in baking enamels. These enamelsare highly resistant to normal alkali metal solutions, but can bereadily removed by the process of this invention.

Melamine modified alkyd resins are also extensively used at the'presenttime and can be readily removed by the process and composition of thepresent invention. Finishes of this type are produced by cookingtogether a melamine urea resin, pentaerythn'tol or glycerol, phthalicanhydride, and a drying oil, such as tung oil, cottonseed oil or thelike.

The epoxy resins are. used on many home appliances and are typicallyproduced from epichlorohydrin, bisphenol and a drying oil. The straightepoxy'resins are crosslinked with a diamine, such as ethylene diamineand can be dried at room temperature or an elevated temperature.resistant to most solvents but can be removed by the process andcomposition of this invention.

The following are typical examples of the present process and ofsuitable cleaning solutions embodying the features of the presentinvention:

Twelve (12) ounces by weight of the above compositions were diluted withwater to make up one gallon of Finishes of this type are exceptionallycleaning solution. This solution was used at its boiling point to stripan enamel finish consisting of alkyd urea melamine containing titaniumdioxide as the white pigment from refrigerator panels and electricautomatic 7 ironer panels. The panels were immersed in the cleaningsolution for seven (7) minutes and the panels were then rinsed withwater.

metal surface was completely broken and the coating was The metalcompletely rinsed from the metal with water.

condition for immediate refinishing.

The bond between the enamel and the I;

" After three minutes, the part was removed and rinsed and the finishthereof was entirely free of paint and 1 surface was left extremelyclean and was in excellent pigment film and was in condition forimmediate re- A solution of the same total concentration and-using thesame alkali stripping compound was made up without adding the sodiumgluconate. Enameled stripportions from the samestock of panels wereimmersed for 45 minutes in this solution, heated to the boiling point.The panels were then rinsed several times with water withoutsatisfactorily removing the finish from the panels.

Example 11 1 Ounces (by weight) Sodium hydroxide 6.64 Sodiummetasilicate 0.8 Sodium resinate 0.4 Cresylic acid 0.24 Sodium gluconate0.4

Eight (8.) ounces by weight of the above composition may be diluted withwater to make one gallon of cleamng solution.

Example Ill Twelve ounces of solid caustic soda were addedto one gallonof water and heated to a rolling boil. In this solu, tion was suspendeda section cut from a standard autofor three minutes, all of the finishwas completely rewater.

mobile interior window molding having a modified alkyd finish. Afterthree minutes, the section was withdrawn and rinsed with a stream ofwater. A film of pigmentre, mained on the surface of the part. Afterrinsing, the part required brushing and scraping to remove the bulk ofthe finish. Thereafter a film adhered to the surface which could not beremoved without vigorous mechanical abrasion.

Example IV 47 grams /2 mole) of aniline were mixed with 196 grams /2mole) of gluconic acid. The gluconic acid;

was in a 50 percent by weight water solution. To the aniline andgluconic acid solution was added 480 grams of water.

The test of Example III was repeated except that 1.2 ounces of theaniline gluconate, prepared as above, was

added to the caustic soda solution.- A section of the same stock used inExample 111 was then immersed in; the solution for a period of three mintes.- It was there after rinsed with water. The metal was completelyfree of paint and pigment film and was immediately in condition forrefinishing.

- Example. V

Example III was repeated using 12 ounces' of a modi fied caustic sodasolution in one gallon .of water. This modified caustic soda solutionhad the following com position in percent by weight:

The above solution was heated to a rolling boil and a finished partcorresponding to those used in Examples I III and IV was immersed in theboiling solution. After three'minutes, the part was withdrawn andrinsed. 'The' metal surface was covered with a thin film of pigmentsimilar to that of Example III which required brushing, scraping andvigorous mechanical abrasion to make 7 the surface suitable forrefinishing.

Example VI. H Twelve ounces of the modified sodium hydroxide cleaningsolution of Example V were added to a gallon of 1.2 ounces of theaniline gluconate prepared as in Example IV were added to this solution.The latter was heated to a rolling-boil and a part similar to-those ofthe above examplesTwas immersed in the solution.

fimshmg' Example VII instead of sodium hydroxide. In this example, 12ounces of potassium hydroxide were dissolved in one gallon of a waterand 1.2 ounces of aniline gluconate were added to the potassiumhydroxidesolution. After immersion of a similar part to those usedin the examplesabove moved from the surface of the part and the surface was I I incondition for refinishing without scraping, brushing or utes, the finishwas readily removed by a water wash the like Example VIII Example IV wasrepeated except that equal molar quantities of furfuryl amine wassubstituted for the ani--- line. Upon immersion of a similar part forthree minand the part was in conditionfor refinishing. 7 Example. IX Vtained.

7 Example X Morpholine was substituted in the same mole ratio foraniline in Example IV. Similar results were obtained.

Example XI Twelve ounces of caustic soda were dissolved in one gallon ofwater. To this solution was added Spercent by weight of gluconic acidand an equal molar quantity of acetone cyanohydrin. The resultingsolution was brought to a rolling boil and a part similar to thatemployed in the above examples was immersed for three minutes. Uponremoval and washing with water, all traces of the finish and pigmentwere completely removed from the part.

When aniline, ethylarnine, dipropylamine, tributylamine, monoisopropanolamine, diisopropanol amine, triisopropanol amine urea, dipropylenetriamine, diethylthiourea, cyclohexyl amine or hexamethylene tetramineare substituted for aniline in Example IV, generally similar results areobtained.

Example XII metal hydroxide in water. This solution was then sepa- 30rated into equal parts. To one part gluconic acid or a derivative wasadded and the second part was employed as a. control. Sections ofduplicate parts were contacted with the two solutions and the time notedin each case which was required to remove the finish from the part. 35

The composition of the stripping solution in Table II corresponded tothat employed in Example I above.

1 Percent by weight oi the total solution in water. 3 Percent by weightof the weight of the alkali metal hydroxide. Moles per mole of gluconicacid.

The preferred finish remover composition of this invention containsother materials, such as surface active agents, sequestering agents,dispersing agents and suspending agents. The following aqueouscompositions are preferred. All quantities are in percent by weight.

Alkali metal hydroxide 3-50 Alkali metal metasilicate 0.5--10 Alkalimetal resinate 0.2-10 Water soluble gluconate 03-10 The abovecomposition can also contain a quantity of an amine, preferably equal tostoichiometric quantities, based on the weight of the water solublegluconate.

TABLE I Alkali Metal Gluconate Time (Minutes) Number Finish type RemarksType Percent 1 Type Percent 2 Contact 3 Water rinse.

5 Acid--. 0. 1 20 1 Alkyd urea Finish completely removed.

melamine. 5 None.... 60 Heavy pigment film remained. Acid 0. 1 9 Finishcompletely removed. 10 None. 30 Heavy pigment film remained. Acid. 0. l3% Finish completely removed. 15. None- 30 Heavy pigment film remained.Acid. 0.1 2 Finish completely removed. 20 None. 30 Heavy pigment filmremained. Acid. 0 1 1% Finish completely removed. 25 None. Heavy pigmentfilm remained. 3O Acid.. 0 1 Finish completely removed. 30 None. 30Heavy pigment film remained.

1 Weight percent of total weight of solution. 1 Weight percent based onweight of alkali metal hydroxide. 4 Time required to remove finish.

TABLE 11 Panel Stripping Composition Number 12 ounces/gal. of compo-Control composition of Color Finish type sition of Example 1, Example I1 1 Black- Soya resin, tung oil, Completely removed in Removed finishin- 6 ester gum and mel- 5minutes. minutes. amine, with primer. Removedprimer in 12 minutes. 2 Blue Lacquer, nitrocelluloseRemovedflnishiniimin. Removed finish in 4 cocoanut alkyd with 1 minutes.plasticizer. Removed primer in 5 Removed primer in 15 m minu s. 3 Powderblue.. Soya-melamine Removedfinishinfimin. Removed finish in 13 minutes.

I In each case a heavy pigment film remained on the surface.

What is claimed is:

1. A process for stripping a colored synthetic resin finish of the typeconsisting of alkyd resins and epoxy resins which leave an adherentpigment deposit on a finished surface when treated with concentratedalkali metal hydroxide solutions, comprising the steps of contacting thefinish with an aqueous solution consisting essentially of water, betweenabout 3 and about 50 weight percent of an alkali metal hydroxide, andbetween about 0.3 and about 10 weight percent of a water solublegluconate for a time sufficient to loosen the finish from the surfaceand completely break the bond between the finish and said surface, andthereafter removing said loosened finish completely from said surface.

2. The process of claim 1 wherein said aqueous solution also containsfrom about 0.5 to about 10 weight percent of a water softening agentselected from the group consisting of alkali metal silicates andphosphates.

3. A process for stripping a synthetic resin finish which leaves anadherent pigment deposit on a finished surface when treated with strong,alkali metal materials, comprising the steps of contacting the finishwith an aqueous solution consisting essentially of water, between about3 and 50 weight percent of an alkali metal hydroxide, between about0.5-1() weight percent of a material selected from the group consistingof sodium metasilicate and trisodium phosphate, between about 02-10weight percent of an alkali metal resinate and between about 0.340weight percent of a water soluble gluconate for a time sufiicient toloosen the finish from the surface, and thereafter removing saidloosened finish from the surface.

4. A process for stripping a snythetic resin finish which leaves anadherent pigment deposit on a finished surface when treated with strong,alkali metal materials, comprising the steps of contacting the finishwith an aqueous solution consisting essentially of water, between about3 and 50 weight percent of an alkali metal hydroxide, between about05-10 weight percent of sodium metasilicate, between about 0.2 weightpercent of an alkali metal resinate and between about 03-10 weightpercent of a water soluble gluconate for a time sufficient to loosen thefinish from the surface, and thereafter removing said loosened finishfrom the surface.

5. A stripping solution for removing colored synthetic resin finisheswhich leave an adherent pigment deposit on a finished surface whentreated with strong alkali materials, the solution consistingessentially of an aqueous solution of water, between about 33-50 percentby weight of an alkali metal hydroxide, between about 0.5-10 percent byweight of a material selected from the group consisting of alkali metalmetasilicates and trialkali metal phosphates, between about 02-10percent by weight of an alkali metal resinate and between about 0.340percent by weight of a water soluble gluconate.

6. The stripping solution of claim 5 wherein the gluconate is an aminegluconate.

7. The stripping solution of claim 5 in which the alkali metal hydroxideconcentration is between about 15-25 percent.

8. A stripping solution of claim 5 wherein the concentration of thealkali metal gluconate is between about 0.3-3.0 weight percent of thealkali metal hydroxide.

9. The stripping solution of claim 6 wherein the amine gluconate is anaromatic amine gluconate.

10. The stripping solution of claim 9 wherein the aromatic aminegluconate is a heterocyclic amine gluconate.

11. The stripping solution of claim 10 in which the heterocyclic aminegluconate is furfuryl amine gluconate.

12. The stripping solution of claim 10 in which the heterocyclic aminegluconate is morpholine gluconate.

13. A stripping solution for removing colored synthetic resin finisheswhich leave an adherent pigment deposit on a finished surface whentreated with strong alkali materials, the solution consistingessentially of an aqueous solution of water, between about 3-50 percentby weight of an alkali metal hydroxide, between about 05-10 percent byweight of an alkali metal metasilicate, between about 0.2-10 percent byweight of an alkali metal resinate, and between about 03-10 percent byweight of a water soluble gluconate.

14. The stripping solution of claim 13 wherein the gluconate is an aminegluconate.

References Cited in the file of this patent UNITED STATES PATENTS FranceMay 31, 1943

5. A STRIPPING SOLUTION FOR REMOVING COLORED SYNTHETIC RESIN FINISHESWHICH LEAVE AN ADHERENT PIGMENT DEPOSIT ON A FINISHED SURFACE WHENTREATED WITH STRONG ALKALI MATERIALS, THE SOLUTION CONSISTINGESSENTIALLY OF AN AQUEOUS SOLUTION OF WATER, BETWEEN ABOUT 3-50 PERCENTBY WEIGHT OF AN ALKALI METAL HYDROXIDE, BETWEEN ABOUT 0.5-10 PERCENT BYWEIGHT OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF ALKALI METALMETASILICATES AND TRIALKALI METAL PHOSPHATES, BETWEEN ABOUT 0.2-10PERCENT BY WEIGHT OF AN WEIGHT OF A WATER SOLUBLE GLUCONATE.